1. Field of the Invention
The present invention relates to an LC filter, and more particularly, to a laminated LC filter for use with high frequencies.
2. Description of the Related Art
In general, a band pass filter that allows a signal of a specific frequency band to pass through includes a plurality of LC resonators. A configuration of one example of a conventional band pass filter is shown in FIG. 13. As shown in FIG. 13, the band pass filter 1 includes the first and second stage LC resonators Q1 and Q2 within a laminate body constructed of layered ceramic sheets 3.
The inductances of the LC resonators Q1 and Q2 are generated by the inductor patterns 4a, 4b, 5a, and 5b. The capacitances of the LC resonators Q1 and Q2 are generated by the capacitor patterns 6a to 6c, 7a to 7c, and the inductor patterns 4a, 4b, 5a, and 5b are arranged on the surface of the ceramic sheets 3 such that the inductor patterns 4a, 4b, 5a, and 5b do not contact the capacitor patterns 6a to 6c, 7a to 7c. The above-described LC resonators Q1 and Q2 are electro-magnetically coupled together.
A leading edge of the inductor pattern 4a is connected to an input lead pattern 14 that is provided on a left side of the sheet 3. A leading edge of the inductor pattern 5a is connected to an output lead pattern 15 that is provided on a right side of the sheet 3. The inductor patterns 4a, 4b, 5a, and 5b and the capacitor patterns 6a to 6c and 7a to 7c are arranged in a layered configuration with alternating layers. The shielding patterns 12a and 12b are provided on either side of this layered configuration.
FIGS. 14 and 15 illustrate another example of a conventional laminated band pass filter. This band pass filter 21 includes first and second stage LC resonators Q1 and Q2 within a laminate body 41 constructed of layered ceramic sheets 23.
The inductances of the LC resonators Q1 and Q2 are generated by the inductor patterns 24 and 25. The capacitances of the LC resonators Q1, Q2 are generated by the capacitor patterns 26 and 27, and the leading edges 24a and 25a of the inductor patterns 24 and 25 are arranged on the surface of the ceramic sheets 23 such that the inductor patterns 24 and 25 do not contact the capacitor patterns 26 and 27. The above-described LC resonators Q1 and Q2 are electrically coupled by a coupling capacitor that is provided by these inductor patterns 24 and 25 and the coupling capacitor pattern 28 that is located opposite to these inductor patterns 24 and 25. These LC resonators Q1 and Q2 are capacitive-coupled to an input lead pattern 29 and an output lead pattern 30, respectively. The shielding patterns 32a and 32b are provided on either side of the layered patterns 24 to 30.
In the laminated body 41, an input terminal electrode 42, an output terminal electrode 43 and shielding terminal electrodes 44 and 45 are provided as shown in FIG. 15. An input lead pattern 29 is connected to the input terminal electrode 42, and an output lead pattern 30 is connected to the output terminal electrode 43. The lead portions of the inductor patterns 24 and 25 and the end portions of the shielding pattern 32a and 32b are connected to the shielding terminal electrode 44. The lead portions of the capacitor patterns 26 and 27 and the other end portions of the shielding pattern 32a and 32b are connected to the shielding terminal electrode 45.
The band pass filter 1 as shown in FIG. 13 is laminated such that the inductor patterns 4a to 5b are sandwiched by the capacitor patterns 6a to 6c, 7a to 7c, so that electric currents flow into each of the inductor patterns 4a, 4b, 5a, and 5b from two capacitor patterns arranged on both sides. Accordingly, the amount of electric current (a current density) flowing through the inductor patterns 4a to 5b increases. As a result, relatively poor Q characteristics of the LC resonators Q1 are Q2 are produced.
Further, in the band pass filter 21 as shown in FIGS. 14 and 15, the magnetic field H generated in the vicinity of the inductor patterns 24 and 25 does not effectively utilize the area S enclosed by a dotted line in FIG. 16 as a magnetic path. As a result, the inductances of the LC resonators Q1 and Q2 are small. Additionally, because the magnetic field H is concentrated at the edges of the inductor patterns 24 and 25, substantial eddy current loss arises, and thus, poor Q characteristics are produced.
Moreover, as shown in FIG. 17, the magnetic field H generated in the vicinity of the inductor patterns 24 and 25 is blocked by the coupling capacitor pattern 28 and the input/output lead patterns 29, 30. Accordingly, the inductances of the LC resonators Q1, Q2 are also reduced.
In order to overcome the problems described above, preferred embodiments of the present invention provide a laminated LC filter having a greatly increased inductance and an excellent Q characteristic.
According to one preferred embodiment of the present invention, a laminated LC filter includes a laminated body including a plurality of insulation layers stacked on each other, a plurality of inductor patterns, and a plurality of capacitor patterns. The laminated LC filter further includes a plurality of LC resonators having a plurality of inductors constructed of inductor patterns, and a plurality of capacitors in which capacitor patterns are arranged such that the capacitor patterns do not contact the inductor patterns, at an inside of the laminated body. The inductor of each LC resonator has a multiplex structure defined by laminating two or more of the inductor patterns having approximately the same shapes via the insulation layers, and coupling capacitor patterns for capacitive-coupling between the LC resonators are laminated between the inductor patterns of the inductors.
In one preferred embodiment of the present invention, capacitor patterns for an input/output are laminated between the inductor patterns of the inductors.
Preferably, three or more stages of filters are provided by connecting at least three of the LC resonators. The pattern widths of the inductor patterns defining the LC resonators at locations other than both ends thereof are wider than the pattern widths of the inductor patterns defining the LC resonators at both end locations. Further, the pattern widths of the inductor patterns defining the LC resonators are reduced at the ends thereof.
A preferred embodiment of the present invention further includes patterns for pole adjustment which are laminated between the inductor patterns of the inductors.
With the above-described configuration, no magnetic field is generated between two or more of the inductor patterns having approximately identical shapes which constitute the respective inductors. Further coupling capacitor patterns and/or capacitor patterns for an input/output that are arranged between the inductor patterns do not block the magnetic field of the inductors.
Moreover, by constructing the inductor to have a multiplex structure, the magnetic field generated in the vicinity of the inductor is alleviated from being concentrated at the edge of the inductor patterns. Further, the inductor patterns in the respective LC resonators correspond to the capacitor patterns at least one-to-one. As a result, the amount of electric current flowing into the respective inductor patterns from the capacitor patterns is much less than in the conventional LC filter. Accordingly, the current density flowing through the inductor patterns is reduced, and the Q characteristic of the respective LC resonators is greatly improved.
Further, the laminated LC filter according to a preferred embodiment of the present invention includes three or more stages of filters which are constructed by connecting at least three of the LC resonators, and the pattern widths of the inductor patterns defining the LC resonators at locations other than both ends thereof are wider than the pattern widths of the inductor patterns defining the LC resonators at both end locations. Further, the pattern widths of the inductor patterns defining the LC resonators are reduced at the ends thereof. Usually, for the inductor patterns that constitute the LC resonator, the magnetic field concentration at the edges of the inductor patterns in the vicinity of the ends thereof is less than the magnetic field concentration at the edges of the inductor patterns in the remainder of the inductor pattern. Further, The magnetic field concentration at the edges of the inductor patterns defining the LC resonators at locations other than both ends thereof is larger than the magnetic field concentration at the edges of the inductor patterns defining the LC resonators at both end locations. By configuring the patterns widths of the inductor patterns of the LC resonators at locations other than both ends to be wider, the magnetic field concentration at the edges of the inductor patterns of the LC resonators at locations other than both ends thereof is reduced.
Therefore, by reducing the width of the inductor pattern at the ends thereof, the magnetic field at the edges of the inductor patterns is reduced.
Moreover, by laminating the patterns for a pole adjustment between the inductor patterns of the inductors, the pole position of the filter is set easily, without blocking the magnetic field generated in the vicinity of the inductors.
Other features, elements, characteristics and advantages of the present invention will become apparent from the detailed description of preferred embodiments thereof with reference to the drawings attached hereto.